In ongoing clinical trials here at the Rockefeller Unversity conducted by the Aaron Diamond AIDS Research Center, combination antiviral regimens have reduced viral RNA levels in plasma to levels below detection. The goal of this study is to ascertain the effects of therapy on the amount of virus in CSF of HIV infected subjects at various stages of HIV infection and therapy. Subjects will either already be enrolled in one of the therapeutic trials in progress here at the Rockefeller University Hospital or be involved in screening for such.